Bleaching poplar groundwood



Patented June 21, 1949 BLEACHING POPLAR GROUNDWOOD Kenneth A. Craig,Appleton, Wis., assignor to Paper Patents consin Company, a corporationof Wis- No Drawing. Application December 4, 194.6, Serial No. 713,917

2 Claims.

The present invention relates to poplar groundwood and more particularlyto the bleaching of poplar groundwood for use in the paper industry.

Illustrative species of woods known in the trade as poplar are Populus:tremoloides, balsamifera, grandidentata, deltoides, heterophylla andtrichocarpa. These poplar woods sometimes referred to as aspen, balsampoplar, large tooth aspen, cottonwood, swamp and black cottonwoodrespectively, have not been used as a source of mechanical or groundwoodpulp for high grade book paper furnishes and the like because of thehigh percentage of decay or rot in standing trees. This decay, acharacteristic of every kind of poplar and known as sap and heart rot orbrown rot, produces dirty and specky groundwood pulp making the sameunfit for use in high grade furnishes or in the manufacture of white orlight colored papers.

The rot is caused by fungi such as false tinder fungus (Fomesigm'arz'us), butt-rot fungus (Fomcs dpplanatus), etc. and as it as ageneral rule attacks the heart or center of the trees it is difficult ifnot impossible to ascertain contamination or decay by an inspection ofthe standing trees. This property of the fungi makes the use of rot-freepoplar economically impractical due to high cost of cutting, examinationthereafter with sorting out of wood containing rot, etc. In view of thiscoupled with the danger of spoiling or rendering unusable a batch ofgroundwood by failure to discover the presence after cutting of even avery small amount of rot, it has been found commercially impractical touse poplar as a source for high grade mechanical pulps. This presentedthe paper industry with an acute problem, for poplar, a wood availablein large amounts, yields a white groundwood fiber of the type desired.

The principal object of the present invention is to provide a processfor producing improved poplar groundwood adaptable for use in high gradefurnishes in the paper industry.

Other objects will be apparent as the description proceeds hereinafter.

At the start of the investigation leading to the present invention itwas discovered that the fungi rots of the poplar were complexcompositions having peculiar properties. Some chemicals such as sulphurdioxide (S02), although capable of bleaching ordinary woods, were foundto have substantially no bleaching effect on fungi rot.

After a prolonged research investigation I discovered that poplargroundwood containing the fungi or brown rot may be rendered usable inhigh grade furnishes by subjecting the groundwood to an initial alkalinehypochlorite bleaching treatment followed by a subsequent acidifying oracid treatment, both treatments being carri d out within the criticallimits set forth below. The following examples will serve to illustratethe present invention.

General example Poplar groundwood slurry of about 2-40 per cent 0. D.(oven dry) consistency and at a temperature of about 25-50 C. is treatedwith an aqueous solution of an alkaline material such as sodiumhydroxide, sodium carbonate and calcium hydroxide, and a hypochloritesuch as an alkaline earth or alkali metal salt, e. g. calciumhypochlorite. Sufficient of the hypochlorite is used to provide about7-15 per cent of available chlorine on the O. D. groundwood basis. Thehypochlorite is usually mixed with the groundwood in a relatively shorttime although the hypochlorite may be added intermittently or moreslowly thereby requiring a longer time for the complete addition. Aportion of the alkaline constituent may be mixed with the hypochloriteand the remainder added separately or the alkaline constituent may beadded simultaneously with and continuously or intermittently after thehypochlorite. Suflicient quantities of the alkaline material (sodiumhydroxide is preferred as it yields the best results) are used toprovide and maintain a pH of about 9-1l during the bleaching reaction.

It has been found necessary to maintain the pH within the above rangeduring the major portion of the bleaching process. A more alkalinecondition results in a discoloration of the pulp which bleaches withgreater difiiculty and a pH value appreciably below 9.0 causes thegroundwood pulp to acquire a reddish coloration resembling chlorination,and results in the consumption of more chlorine to obtain the sameresuit. The bleaching action is allowed to proceed until the availablechlorine is essentially consumed which requires from 10 minutes toseveral hours depending upon the consistency, temperature, pH, per centavailable chlorine used, etc., and the mixture is subjected tointermittent or preferably continuous agitation during the bleachingaction.

After the hypochlorite treatment and the available chlorine issubstantially consumed, a necessary condition in order to prevent theformation of the reddish coloration, the groundwood mixture isacidified, i. e. the pH is lowered or made acid. by addition of anacidic material to a pH of 4.0-7.0 with a pH of 5.0-5.5 being preferred.The acidic materials include acid bisulfites and mineral acids as wellas organic acids, sulfurous acid and alum being two preferred materials.The mixture after acidification may or may not be washed prior to usingin paper furnish in accordance with the standard practices in the paperart.

Example According to the above procedure, an aqueous slurry of rotinfected groundwood at about 5 per cent consistency was placed in a tankand treated at a temperature of about 40 C. with an aqueous solution ofcalcium hypochlorite. The available chlorine, based on the groundwood,was about 10.7 per cent. This is in accordance with the preferredprocedure employing approximately per cent available chlorine based onthe groundwood. Sodium hydroxide was added continuously to thegroundwood-calcium hypochlorite mixture so as to maintain the reactionmixture at a pH of about 10.5. The treatment was continued until theavailable chlorine was consumed, which took about 20-30 minutes. Thealkaline reaction mixture was then pumped into a storage chest fromwhence it was continuously pumped into an acidification tank and mixedwith sufficient sulphurous acid to bring the pH of the slurry down toabout 5.0-5.5.

In one months commercial operation of the above process, about 1,236tons (air-dry basis) of poplar groundwood contaminated by fungi or brownrot was treated using about 378.2 tons of calcium hypochlorite(containing 35 per cent available chlorine) and about 58.7 tons ofsodium hydroxide. From this operation 1,198 tons (air-dry basis) ofwashed, bleached groundwood pulp was obtained. This data shows a loss ofabout 38 tons, which means a yield of about 97 per cent.

Investigations show that poplar groundwood pulp bleached in accordancewith the preferred conditions of the present invention has a brightnessof 74-75 as measured on the General Electric Reflectance Meter and thatthe bleached pulp even when the original wood contains relatively largeamounts of fungi rot is adaptable for use in high grade news and bookpaper furnishes. Investigations also show that the fiber strength ofpoplar groundwood is not deleteriously affected by the bleachingtreatment of the present invention. Investigations further show thatvery small loss (less than 1 per cent in small oper ations and about 3per cent in large scale commercial operations) is experienced as aresult of the chemical treatment of the poplar groundwood in accordancewith the present invention.

The poplar groundwood treated in accordance with the present inventionin addition has been found particularly adaptable for use in paper withalkaline fillers or coating pigments such as calcium carbonate. While nofiller is formed when sodium hydroxide is employed as the alkalinematerial, it will be noted that calcium car-- bonate filler may beformed in situ by employing sodium carbonate as the alkaline materialin.

4 combination with calcium hypochlorite. Alkaline fillers or pigments,due to discoloration, are not as a general rule adaptable for use withgroundwood or mechanical pulps containing all the constituents of theoriginal wood.

Large scale operations show the hypochlorite bleaching treatment of thepresent invention to be economically and commercially practical. Theloss during the chemical treatment of poplar is unexpectedly low andcommercial operations show that the process of the present inventionprovides the art with a satisfactory means for utilizing poplargroundwood in high grade paper furnishes.

This application is a continuation in part of my co-pending application,Serial No. 388,803 filed April 16, 1941, now abandoned.

I claim:

1. In the paper art, the process of treating poplar groundwoodcontaminated with fungi rot which comprises subjecting the contaminatedgroundwood to the action of an alkaline hypochlorite solution having apH value of about 9-11 and a temperature of about 25-50 C., sufficienthypochlorite being present to provide about 715 per cent availablechlorine based on the groundwood, and then acidifying said solutionafter the consumption of the available chlo- 2. In the paper art, theprocess of treating poplar groundwood contaminated with fungi rot, whichcomprises subjecting the contaminated groundwood to the bleaching actionof an aqueous sodium hydroxide-calcium hypochlorite solution at atemperature of about 25-50 (3., said solution having a pH value about9-11 and containing sufficient hypochlorite to provide about 7-15 percent available chlorine based on the groundwood, and after theconsumption of the available chlorine subjecting said groundwood to anacid treatment by addition of sulphurous acid to said solution.

KENNETH A. CRAIG.

REFERENCES CITED The following referenlces are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 11,786 Horsford Oct. 10, 1354348,165 Just et a1. Aug. 24, 1886 481,414 Myrick Aug. 23, 1892 1,468,693Baker Sept. 25, 1923 1,645,061 Kress Oct. 11, 1927 2,020,437 Smith Nov.12, 1935 2,046,382 Hirschkind July 7, 1936 2,187,016 Craig Jan. 16, 19402,359,891 Brallier et a1. Oct. 10, 1944 FOREIGN PATENTS Number CountryDate 298,333 Great Britain Oct. 11, 1928 OTHER REFERENCES Munro-TheGrinding of Wood Infected by Fungi, Paper Industry, July 1920, page 564.

